Induction of Biplanar Growth in Fern Gametophytes

In constant white light, protonemata of different ages of Asplenium nidus produce a fixed number of cells before they become biplanar. Protonemata with a lower initial cell number require a longer time to become biplanar than those with a higher initial cell number. Increasing the photoperiod or the light intensity reduces the cell number in the filament at the time of initiation of biplanar morphology. It is suggested that inductive light acts directly on cell metabolism to induce biplanar morphology, rather than indirectly by inducing mitotic activity.     

In vitro Phytohormonal Regulation of Fern Gametophytes Growth and Development

Russian Journal of Developmental Biology - Interest in ferns as objects of biotechnological research is determined by the characteristics of their development and reproduction, which is important...     

Dark Growth and the Associated Phenomenon of Age-dependent Photoresponses in Fern Gametophytes

The cross-sectional area of the growing tip of a fern filamentundergoes an age-dependent decline over the period of darknessthat precedes an experimental light treatment. This dark-mediateddecline accounts for the appearance of age-dependent responsesto light treatments. Moverover, monochromatic irradiation experimentsshow that the cross-sectional areas of filaments do not manifestsignificant age-dependent variation in response to light treatmentsof sufficient energy. Because it is the cross-sectional arearather than the elongation rate that exhibits the direct responseto light in the control of filament growth, it follows thatthere is no evidence for age-dependent changes in photosensitivityof the filaments. Regression analyses establish that pre-germinationlight treatments do not affect subsequent patterns of dark growth;instead, stress calculations suggest that the tapering of thecross-sectional area may be referable to a state of stress-straindisequilibrium within the filament tip. These and other characteristicsof age-dependent growth responses of fern filaments are summarizedin a general working model. fern gametophytes, age-dependent photoresponses, stress analysis, Onoclea sensibilis     

An Evaluation of Specific and Non-Specific Inhibition of 2-Dimensional Growth in Fern Gametophytes

Gametophytes of Onoclea sensibilis were grown under continuous white light of 90 lux. Filaments were produced having 4–6 cells before the initiation of 2-dimensional growth. There was a close correlation between the average cell number of a population of plants and the proportion of 2-dimensional forms. 8-Azaguanine produced a general inhibition of growth, and it was shown that the reduced proportion of 2-dimensional plants caused by 8-azaguanine was a secondary consequence of the general growth inhibition. IAA however gave a true specific inhibition of 2-dimensional growth. Based on these experiments the proper criteria for establishing a specific inhibition of 2-dimcnsional growth arc discussed. These criteria are applied in a critical review of previous papers on the inhibition of 2-dimensional growth. It is concluded that no firm evidence is available that inhibition of protein synthesis specifically blocks 2-dimensional growth.     

Effects of Colchicine and Light on Cell Form in Fern Gametophytes. Implications for a Mechanism of Light-induced Cell Elongation

Spores of the fern, Onoclea sensihilis L., suffer a disruption of normal development when they are cultured on media containing colchicine. Cell division is inhibited, and the spores develop into giant spherical cells under continuous white fluorescent light. In darkness only slight cell expansion occurs. Spherical cell expansion in the light requires continuous irradiation. Photosynthesis does not seem to be involved, since variations in light intensity do not affect the final cell diameter; the addition of sucrose to the medium does not permit cell expansion in darkness; and the inhibitor DCMU does not block the light-induced cell expansion. Continuous irradiation of colchicine-treated spores with blue, red or far-red light produces different patterns of cell expansion. Blue light permits spherical growth, similar to that found under white light, whereas red and far-red light promote the reestablishment of polarized filamentous growth. Although ethylene is unable to induce polarized cell expansion in colchicine-treated spores in darkness or white and blue light, it enhances filamentous growth which already is established by red or far-red irradiation. Both red and far-red light increase the elongation of normal filaments (untreated with colchicine) above that of dark-grown plants, but under all 3 conditions the rates of volume growth are identical. Light, however, does cause a decrease in the cell diameters of irradiated filaments. These data are used to construct an hypothesis to explain the promotion of cell elongation in fern protonemata by red and far-red light. The model proposes light-mediated changes in microtubular orientation and cell wall structure which lead to restriction of lateral cell expansion and enhanced elongation growth.     

蕨类植物配子体育及其性器官分化的研究进展

作者概述了蕨类植物生活周期中不同发育阶段的特点,并着重介绍了不,植物生长调节物质,水和温度等因素对蕨类植物配子体发育的影响以及精子囊素,光,钙离子和其它植物生长调节物质在性器官形成和分化过程中的作用,同时作者对蕨类植物性器官分化的不稳定性进行了探讨,并结合目前蕨类植物性器官分化的遗传学和分子生物学研究的最新进展,说明蕨类植物作为研究系统在植物生物学研究领域中的优势。     

蕨类植物配子体发育及其性器官分化的研究进展

作者概述了蕨类植物生活周期中不同发育阶段的特点,并着重介绍了光、植物生长调节物质、水和温度等因素对蕨类植物配子体发育的影响以及成精子囊素、光、钙离子和其它植物生长调节物质在性器官形成和分化过程中的作用。同时作者对蕨类植物性器官分化的不稳定性进行了探讨、并结合目前蕨类植物性器官分化的遗传学和分子生物学研究的最新进展,说明蕨类植物作为研究系统在植物生物学研究领域中的优势。     

Photosynthetic Rates of Sporophytes and Gametophytes of the Fern, Todea barbara

The photosynthetic rates of intact sporophytes or gametophytes of the fern Todea barbara grown in sterile culture were measured using an infrared gas analyzer. Sporophytes consisted of single whole plants with roots and leaves grown in tubes of agar. Gametophytes were grown as several plants covering the surface of the agar. Sporophytes had photosynthetic rates at light saturation of 8.50 microliters CO₂ per hour per milligram dry weight and 1,300 microliters CO₂ per hour per milligram chlorophyll, whereas rates for gametophytes were lower, 2.36 microliters CO₂ per hour per milligram dry weight and 236 microliters CO₂ per hour per milligram chlorophyll.     

Palynology of the Genus Passerina (Thymelaeaceae): Relationships Form and Function

Pollen of the genus Passerina L. differs markedly from that of other southern African members of the Thymelaeaceae. Grains of most members of the Thymelaeaceae are characterised by a typical croton pattern, comprising rings of more or less trihedral sexine units mounted on an underlying reticulum of circular muri. In Passerina, however, the supratectal subunits are fused completely to form a continuous reticulum, which replaces the underlying reticulum. The reticulum in Passerina is therefore secondary in origin and not homologous with the basal reticulum of typical crotonoid grains in the family. The croton pattern has often been used as indication of a possible relationship between the Euphorbiaceae and Thymelaeaceae. Pollen of Passerina is adapted to anemophily. Grain sculpturing clearly demonstrates secondary derivation of a reticulate pattern from the typical croton pattern, through reduction, aggregation and fusion. Pollen of Passerina represents a climax of a continuum of variation in the exine of pollen in the Thymelaeaceae. As Passerina is considered phylogenetically advanced in the subfamily Thymelaeoideae, the subtribe Passerininae is raised to tribal rank, namely tribe Passerineae.     

The Photobiology of Fern Gametophytes: I. THE PHENOMENON OF RED/FAR-RED AND YELLOW/F AR-RED PHOTOREVERSIBILITY

This paper shows that the hypothetical yellow-light-absorbingpigment P₅₈₀ is an unnecessary postulate for describing thephotobiology of fern filaments. The existence of P₅₈₀ was originallypredicted on the basis of action and response spectra that assumedthat filament elongation is the growth parameter subject todirect photocontrol. The present work supports an alternativeconcept, that the cross-sectional area at the base of the apicaldome is the photocontrolled parameter. Far-red irradiation reversesthe effects of both red and yellow light, and dose-responsecurves for yellow light parallel but lag behind the curves forred light. These observations indicate that the responses offern filaments to the entire long wavelength spectral region(yellow to far-red) can be attributed to absorption of lightby phytochrome alone.     

乌蕨配子体发育及卵发生的显微观察

采用光学显微镜对乌蕨的配子体发育及卵发生的过程进行了研究,以阐明蕨类植物颈卵器发育特征,为揭示蕨类植物有性生殖机制以及鳞始蕨科的演化提供依据。结果表明:(1)乌蕨孢子黄褐色,具单裂缝,表面平滑或呈疣状纹饰;孢子接种12d萌发,萌发类型为书带蕨型,原叶体发育类型为铁线蕨型。(2)半薄切片观察表明,乌蕨颈卵器产生于原叶体生长点下方的表面细胞,即颈卵器原始细胞,该细胞经过两次分裂形成纵向3层细胞,最上层细胞发育为颈卵器的颈部壁细胞,中间层细胞即初生细胞再经过两次不等分裂产生颈沟细胞、腹沟细胞和卵细胞,此三细胞最初紧密贴合,随着颈卵器的发育,卵细胞与腹沟细胞间从两侧向中间产生分离腔,且腹沟细胞与颈沟细胞开始退化;分离腔逐渐向中间扩大,直至出现孔状结构,即受精孔;颈卵器发育后期,在卵细胞上表面形成染色较深的卵膜,颈沟细胞与腹沟细胞退化成絮状物。     

扇叶铁线蕨配子体发育及卵发生的显微观察

采用显微观察技术对扇叶铁线蕨配子体发育和卵发生进行了研究.结果显示:(1)扇叶铁线蕨孢子黄褐色,四面体形,具三裂缝,孢子接种后4～7 d萌发,经丝状体和片状体阶段发育为心形的原叶体,成熟原叶体雌雄同株,在原叶体基部产生精子器,在原叶体生长点下方产生颈卵器.(2)切片观察表明,扇叶铁线蕨颈卵器产生于生长点下方的表面细胞(颈卵器原始细胞),该细胞经2次分裂形成3层细胞,其上层细胞发育为颈卵器颈部壁细胞,中间细胞为初生细胞,它经2次不等分裂产生3个细胞--卵细胞、腹沟细胞和颈沟细胞;刚产生时, 3个细胞紧贴颈卵器壁,随着发育,卵细胞和腹沟细胞之间产生了分离腔,同时在卵细胞上表面形成了染色深的卵膜;此后,颈沟细胞和腹沟细胞逐渐退化,在颈沟内产生大量不定形物质,受精作用观察表明,该物质能够吸引精子进入颈卵器.(3)连续切片观察发现,成熟卵细胞上表面卵膜中央具有受精孔,表明受精孔在同型孢子蕨类卵细胞中可能是普遍存在的.     

A Role for Purines and Pyrimidines of Ribonucleic Acid in the Induction of Two-dimensional Growth in the Gametophytes of the Fern, Asplenium nidus

The inhibition of two-dimensional growth in the gametophytesof Asplenium nidus induced by purine and pyrimidine analoguesand the reversal of inhibition by natural purine and pyrimidinebases and their derivatives have been studied. Adenine and guanineand their ribosides and ribotides were more effective than cytosine,uracil, thymine, and their derivatives in preventing the inhibitiondue to 8-azaadenine and 8-azaguanine. Likewise, the inhibitoryeffects of 2-thiocytosine, 2-thiouracil,6-azauracil, and 5-fluorouracilwere overcome by the pyrimidines and their derivatives, butnot usually by the purines.Combinations of two purine analoguesor two pyrimidine analogues or one purine analogue and one pyrimidineanalogue inhibited growth more effectively than single compounds.The combined inhibitions were maximally reversed when both naturalbases or their derivatives were added to the medium. It is concludedthat there is a requirement for both purines and pyrimidinesof ribonucleic acid in the induction of two-dimensional growthin the gametophytes of Asplenium nidus.     

The Relationships between Xylem Safety and Hydraulic Efficiency in the Cupressaceae: The Evolution of Pit Membrane Form and Function

Water transport in conifers occurs through single-celled tracheids that are connected to one another via intertracheid pit membranes. These membranes have two components: the porous margo, which allows water to pass through the membrane, and the impermeable torus, which functions to isolate gas-filled tracheids. During drought, tracheids can become air filled and thus hydraulically dysfunctional, a result of air entering through the pit membrane and nucleating cavitation in the water column. What are the hydraulic tradeoffs associated with cavitation resistance at the pit level, and how do they vary within the structural components of the intertracheid pit? To address these questions, we examined pit structure in 15 species of Cupressaceae exhibiting a broad range of cavitation resistances. Across species, cavitation resistance was most closely correlated to the ratio of the torus to pit aperture diameter but did not vary systematically with margo porosity. Furthermore, our data indicate that constraints on pit hydraulic efficiency are shared: the pit aperture limits pit conductivity in more drought-resistant taxa, while increased margo resistance is more likely to control pit conductivity in species that are more vulnerable to cavitation. These results are coupled with additional data concerning pit membrane structure and function and are discussed in the context of the evolutionary biogeography of the Cupressaceae.Water transport in conifers occurs through narrow, single-celled conduits (tracheids) that are organized in overlapping, longitudinal files. This simple, homoxylous arrangement represents an ancestral vascular design that has remained remarkably consistent since its first appearance in the progymnosperms of the Mid-Devonian (Taylor et al., 2009). However, the small size of tracheids can impose a high resistance to water transport as compared with the large, hydraulically efficient vessels present in many angiosperms (Hacke et al., 2004; Sperry et al., 2006). Despite this handicap, conifer tracheids can be just as hydraulically efficient as angiosperm xylem for a given conduit diameter, a result that can be wholly attributed to the distinctive structure of the conifer intertracheid pit membrane (Pittermann et al., 2005; Sperry et al., 2006).Because pit membranes also function to limit the spread of air from one conduit to another (cavitation), the physiological consequences of the transport efficiency versus cavitation safety tradeoffs in conifer and angiosperm pit membranes have received considerable attention at the pit and xylem levels, whereby cavitation resistance in north temperate woody plants appears to come at the cost of hydraulic efficiency (Pittermann et al., 2006a, 2006b; Sperry et al., 2006; Choat et al., 2008; Domec et al., 2008; Jansen et al., 2009; Schoonmaker et al., 2010). Previous work has shown that the integrated vascular performance of plants is key to understanding species distributions (Sperry et al., 1994; Brodribb and Hill, 1999; Pockman and Sperry, 2000; Choat et al., 2007), and within this framework, pit membranes have the potential to act as the nexus of the cavitation safety versus transport efficiency compromise. Yet, despite our progress, we are just starting to learn how these tradeoffs play out at the level of the pit membrane, particularly in one as complex as that of conifers. Hence, the goals of this study were to determine whether selection has acted to optimize conifer pit membrane performance in a manner that reflects species cavitation resistance and habitat distribution as well as to examine the role, if any, of evolutionary lineage.Unlike the homogenous pit membrane of angiosperm vessels, the conifer pit membrane is composed of two distinct regions: a thickened, centrally located torus and a porous margo region that surrounds it (Fig. 1; for study species, see Hacke et al., 2004; Choat et al., 2008; Choat and Pittermann, 2009). When tracheids are water filled, the pit membrane is centrally located in the pit chamber and water moves from tracheid to tracheid through the margo. Should an air-seeding event (cavitation) occur, causing a tracheid to become air filled, (i.e. embolized), the negative xylem pressure in the water-filled tracheid will act on the air-water interface in the margo pores by deflecting the pit membrane in the direction of the functional tracheid, thereby appressing the torus against the pit aperture border (Bailey, 1913; Liese, 1965; Liese and Bauch, 1967; Petty, 1972). This valve action of the membrane can create an effective seal that prevents further spread of air in the xylem. Cavitation is thought to occur when the water potential of the water-filled tracheid becomes negative enough to dislodge the torus from its sealing position, allowing air to enter the conduit. Overall, the structure of the torus-margo pit membrane must optimize what at first glance appear to be conflicting functional requirements: on the one hand, cavitation resistance selects for a combination of large tori and small apertures, but on the other hand, hydraulic efficiency favors porous margos, large apertures, and small tori.Open in a separate windowFigure 1.SEM images of intertracheid pit membranes belonging to nine Cupressaceae species (of 15) that represent the broad range of observed cavitation pressures. The opaque torus region of the membrane (T) is held centrally by the microfibrils of the margo (M). Visually, increased cavitation resistance appears to be associated with increased margo porosity, but quantitative estimates of margo resistance made on the most intact regions of the pit membranes (Fig. 8) revealed no differences among the species surveyed.

Table I.

Study species, figure abbreviations (Fig. Abbrevs.), locations (SFBG, San Francisco Botanical Garden, San Francisco; UCBG, University of California Botanical Garden, Berkeley, CA; UCSC, University of California, Santa Cruz, Arboretum, Santa Cruz, CA), and species natural history (Farjon, 2005)

Arginine Vasotocin: Structure-Activity Relationships and Influence on Gonadal Growth and Function

When AVT (arginine vasotocin) was given neonatally during theperiod when the brain is undergoing sexual differentiation,increased growth of the reproductive organs was observed inadulthood. Injection of AVT after this neonatal period in immatureanimals led to diminished growth of the accessory organs andin some cases the gonads themselves. The hypertrophic responseof the in situ ovary in adult mice following unilateral ovariectomy(UO) was inhibited in a dose-related manner by a single intraperitonealinjection of freshly prepared AVT. Much less AVT was requiredfor this response when injected into the third ventricle. Afterintraperitoneal injection, arginine vasopressin (AVP), lysinevasopressin (LVP), and 4-leucine vasotocin (4-leu-AVT) alsoinhibited compensatory ovarian hypertrophy whereas oxytocindid not. The commonality in die structure of these antigonadotrophicpeptides include a closed ring and a basic amino acid in position8. After opening the disulfide bond of these nonapeptides withmercaptoethanol, a single injection of the reduced AVT, AVP,LVP, or 4-leu-AVT into UO mice causes exaggerated hypertrophyof the remaining ovary. When added with leuteinizing hormone-releasinghormone (LRH) to culture medium containing hemipituitaries fromcastrated estrogen-progesterone primed female rats, AVT significantlyincreased the release of radioimmunoassayable LH above thatdue to LRH alone. AVT might interact at all levels of the hypothalamo-hypophysealgonadalaxis.     

蕨配子体发育及卵发生的显微结构观察

运用显微观察技术对蕨(Pteridium aquilinum var. latiusculum)配子体发育和卵发生进行了研究。结果表明：(1)蕨孢子黄褐色,四面体形,具三裂缝,接种后3～7 d萌发,经丝状体和片状体阶段发育成原叶体,成熟原叶体雌雄异株或同株。(2)蕨颈卵器产生于生长点下方的表面细胞(颈卵器原始细胞),该细胞经2次分裂形成3层细胞,其上层和下层细胞发育为颈卵器壁细胞,中间细胞为初生细胞,它经2次不等分裂产生3个细胞,分别为卵细胞、腹沟细胞和颈沟细胞;刚产生时,此3个细胞紧贴颈卵器壁,细胞质内液泡较多,随着发育,卵细胞和腹沟细胞之间产生了分离腔,但二者通过孔区相连,在卵细胞上表面可观察到卵膜;此后,颈沟细胞和腹沟细胞逐渐退化,颈卵器壁细胞内具有黑色颗粒物质。连续切片观察发现,成熟卵细胞上表面中央具有受精孔。卵发生的细节尚需超微结构的研究。